Fluidic oscillators are well known in the prior art for their ability to provide a wide range of liquid spray patterns by cyclically deflecting a liquid jet. The operation of most fluidic oscillators is characterized by the cyclic deflection of a fluid jet without the use of mechanical moving parts. Consequently, an advantage of fluidic oscillators is that they are not subject to the wear and tear which adversely affects the reliability and operation of other spray devices.
Examples of fluidic oscillators may be found in many patents, including U.S. Pat. No. 3,185,166 (Horton & Bowles), U.S. Pat. No. 3,563,462 (Bauer), U.S. Pat. No. 4,052,002 (Stouffer & Bray), U.S. Pat. No. 4,151,955 (Stouffer), U.S. Pat. No. 4,157,161 (Bauer), U.S. Pat. No. 4,231,519 (Stouffer), which was reissued as RE 33,158, U.S. Pat. No. 4,508,267 (Stouffer), U.S. Pat. No. 5,035,361 (Stouffer), U.S. Pat. No. 5,213,269 (Srinath), U.S. Pat. No. 5,971,301 (Stouffer), U.S. Pat. No. 6,186,409 (Srinath) and U.S. Pat. No. 6,253,782 (Raghu). An oscillating liquid jet can yield a variety of spray patterns for the downstream distribution of the liquid droplets that are faulted as this liquid jet breaks apart in the surrounding gaseous environment.
For the spraying of some high viscosity liquids (i.e., 15-20 centipoise), the “mushroom oscillator” disclosed in commonly owned U.S. Pat. No. 6,253,782 was found to be especially useful. However, it also has been found that, as the temperature of such liquids continues to decrease so as to cause their viscosity to increase (e.g., 25 centipoise), the performance of this type of oscillator can deteriorate to the point where it no longer provides a jet that is sufficiently oscillatory in nature to allow its spray to be distributed over an appreciable fan angle. This situation is especially problematic in automotive windshield washer applications.
An early approach to solving that problem by the instant applicant led to the method and structure of the “Three Jet Island” fluidic circuit of commonly owned U.S. Pat. No. 4,761,036, as illustrated in FIGS. 1A-1Q and incorporated herein by reference. The fluidic circuit geometry of insert 18 (illustrated in FIG. 1G) was more effective than the fluidic oscillators which had come before, but applicants' experiments revealed that for certain kinds of fluids and at certain temperatures, fluidic insert 18, like the other prior art fluidic oscillators in some circumstances may not (a) reliably begin the oscillation inducing fluid dynamic mechanisms or (b) reliably maintain the fluid jet oscillation steering mechanisms within the interaction chamber and both are needed to reliably establish and maintain the desired oscillating spray, especially with cold or viscous fluids.
There is a need, therefore, for an improved method and apparatus for generating sprays of colder, more viscous fluids.